Interpretive Summary: E. coli O157:H7 is one of the major bacterial pathogens associated with foodborne diseases. This pathogen is frequently found in and around cattle and it enters the human food chain when carcasses become contaminated during slaughter/processing and ground beef from such carcasses is consumed without proper cooking. In this study, the effectiveness of current interventions used in reducing the amount of E. coli O157 and other organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of cattle was performed at five locations in each plant. For each sample, E. coli O157 prevalence was determined and generic bacteria, members of the Enterobacteriaceae bacterial family, and E. coli O157 were counted. The incidence of E. coli O157 was reduced from 76% on animal hides coming into the plant to 0% on carcasses leaving the cooler. It was determined that those groups of cattle with high rates of E. coli O157 on their hides also had high rates of E. coli O157 on their carcasses. Generic bacteria counts and Enterobacteriaceae counts were reduced by in-plant interventions to less than 0.0001% of their initial levels. This study shows that those cattle with high levels of generic bacteria and Enterobacteriaceae are more likely to be contaminated with E. coli O157. Implementation of the sampling protocol described herein would allow processors to evaluate the efficacy of on-line antimicrobial interventions as well as allow industry-wide benchmarking of hygienic practices.

Technical Abstract:
The effectiveness of current antimicrobial interventions used in reducing the prevalence/load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of beef cattle was performed at five locations from the initial entry of the animals to the slaughter floor to the exit of carcasses from the ¿hotbox¿ cooler. For each sample, E. coli O157 prevalence was determined and total aerobic bacteria, Enterobacteriaceae, and E. coli O157 were enumerated. E. coli O157 was reduced from an incidence of 76% on animal hides coming into the plant to 0% on carcasses leaving the cooler. A positive relationship was seen between the incidence of E. coli O157 in hide and pre-evisceration samples. Aerobic plate counts (APC) and Enterobacteriaceae counts (EBC) were reduced from 7.8 and 6.2 log CFU/100 cm2 to 1.4 and 0.4 log CFU/100 cm2, respectively. Levels of APC and EBC on carcasses were significantly related to the respective levels on the corresponding hides, with the carcasses of animals whose hides carried higher numbers of bacteria being more likely to carry higher numbers of bacteria. Implementation of the sampling protocol described herein would allow processors to evaluate the efficacy of on-line antimicrobial interventions as well as allow industry-wide benchmarking of hygienic practices.